Method of forming glass film on metal



July 22, 1947. 5, 555 2,424,353

METHOD OF F'O-RIIN'G eLAss FILM-0N METAL Filed Oct. 14, 1944 INVENTOR SANFORD e ESSIG ATTORNEY Patented July 22, 1941 METHOD OF FORMING GLASS FIIM ON METAL Sanford F. Essig, Fort Wayne, Ind., assignor to Farnsworth Television and Radio Corporation, a corporation of Delaware Application October 14, 1944, Serial No. 558,689

I 11 Claims. v 1

This invention relates generally to television tubes, and more particularly to the manufacture of an electrode comprising a semi-conducting layer of uniform thickness on a metallic support. A dielectric layer of semi-conducting material provided on a metallic support is useful in television transmitting tubes, for instance, as a base for a mosaic screen electrode. Conventional mosaic screens have been made by coating an insulating dielectric material, such as a sheet of mica, with a metallic layer which serves as a signal plate. The other surface of the sheet of mica is provided with a photosensitive cathode consisting of discrete metallic particles. The metallic particles and the signal plate form the two plates of a condenser while the mica serves as the dielectric therebetween.

To overcome this serious drawback of the conventional television picture signal generating tube it has been suggested to use a mosaic screen which has a dielectric layer that is electrically semi-conducting. Such a semi-conductive mosaic could be given a biasing voltage to increase the strength of the electric field between the mosaic and the second anode. This field could, for instance, be made of such a strength that all or substantially all of the secondary electrons are attracted and collected by the second anode. In this manner the electron redistribution problem could be solved and at the same time an increase of the picture signal strength could be obtained. On the other hand, when the dielectric material which separates the signal plate from the In a conventional television picture signal gencrating tube of the light storage type such a'mosaic electrode is bombarded by electrons so that secondary electrons are liberated. A comparatively small portion of the secondary electrons is collected by the second anode or collector electrode of the pickup tube. The larger portion oi. the secondary electrons, however, is redistributed over the mosaic screen. In view of the fact that the secondary electrons are not always uniformly distributed over the mosaic they give rise to an undesired background shading of the television picture reproduced in a receiving tube.

It is, therefore, obvious that it would be desirable to collect substantially all secondary electrons 'by the second anode to avoid this background shading efiect and to increase the sensitivity of the pickup tube. This, however, is not possible with the conventional television pickup tube of the light storage type because the strength of the electric field existing between the mosaic and the second anode is too small for that purpose and can not be controlled. The electric field between the mosaic screen and the second anode is small because the equilibrium potential of the mosaic screen shortly after the electron bombardment is very'near the potential of the second anode or collector electrode. Also, the strength of the picture signals generated by the television tube is directly dependent upon the strength of the electric field between the mosaic screen and the second anode until saturation of the secondary electrons takes place.

photosensitive cathode is made of a semi-conducting material, part of the charge which is built up and stored on the photosensitive islands of the cathode through the action of the light is dissipated across the dielectric. This, in turn, tends to decrease the strength of the picture signal generated in the television pickup tube. However, theoretical considerations show that there is an optimum value for the resistance of the dielectric material separating the signal plate from the photosensitive cathode where the strength of the picture signal is at a maximum. According to these calculations the dielectric layer should have a very high resistance and hence should be made of a semi-conducting material.

The principal object of this invention is to provide a novel method of forming a. semi-conductive layer on a metallic support.

It is a further object of the present invention to provide a method of forming a glass film of uniform thickness on a metallic support.

In accordance with the present invention a glass film is formed on a metallic member by first applying glass to a surface of the metallic member, whereupon the glass is covered with a metallic foil. The metallic member, the glass and the foil are heated until the glass is in its plastic state. Then the foil and the metallic member are pressed against each other until the glass fills the space between the metallic member and the foil. Finally, the foil is removed to provide a glass film of substantially uniform thickness on the metallic member.

- In accordance with another embodiment of .3 I the invention a glass film is formed on a metallic base by applying a relatively thick layer of glass to a surface of the base. This glass layer is then covered with a metallic foil, and the metallic base is heated to an elevated temperature. The foil is pressed against the metallic base until the glass layer is in intimate contact with its two metallic covers. Then the foil is peeled off from the base and simultaneously a portion of the glass layer adhering to the foil is removed to reduce the thickness of the glass layer.

In accordance with still another embodiment of the invention two metallic foils are each coated with glass and the foils are then superimposed with their glass coatings in contact. Now the foils are heated until the glass is in its plastic state and then the foils are rolled so that the glass coatings form a continuous glass film of substantially uniform thickness. Finally, one of the foils is removed.

For a better understanding of the invention, together with other and further objects thereof, reference is made to the following description, taken in connection with the accompanying drawing, and its scope will be pointed out in the appended claims.

In the accompanying drawing:

Fig. 1 shows a cross-section of a glass film sandwiched between a metallic foil and a metallic base;

Fig. 2 shows a cross-section of the same structure shown in Fig. 1 and illustrates the removal of the metallic foil;

Fig. 3 shows a cross-section of a glass layer on a metallic base formed in accordance with the invention;

Figs. 4 to 6 illustrate various consecutive steps in the manufacture of a glass film on a metallic foil;

Fig. 7 shows a cross-section of a silver foil bearing a glass layer of uniform thickness; and

Fig. 8 shows a cross-section of amuiiie having rolls therein for rolling a hot glass layer sandwiched between metallic sheets.

Referring more particularly to Fig. 1 of the drawing, there is shown a glass layer I sandwiched between a metallic base 2 and a metallic foil 3. Metallic base 2 as well as metallic foil 3 preferably consists of silver. In accordance with the invention a glass layer of substantially uniform thickness is formed by first applying a relatively thick layer of molten glass to silver base 2. To this end silver base 2 ma be heated to an elevated temperature before the glass layer is applied thereto. Then the glass layer is covered with silver foil 3 which may have a thickness of about .001". Now silver foil 3 is pressed by rolling against silver base 2 and any excess amount of glass is squeezed out as shown in Fig. 1,

The final step in the manufacture of the glass film consists in peeling off silver foil 3 in the direction of arrow 4 shown in Fig. 2. A certain portion of the glass will stick to silver foil 3 and hence will be removed'with the foil. In this manner the thickness of glass layer I is reduced, and the remaining glass layer is about half as thick as glass layer I, Pressing silver base 2 against silver foil 3 not only squeezes out part of the glass and thus reduces the thickness of the glass layer but also insures a more intimate contact between glass layer I and silver base 2 and silver foil 3.

The adhesion characteristics of glass to silver depend upon the surface of the silver. It has been found that an etched silver surface retains the glass better than a smooth silver surface.

It is desired to have glass layer I adhere to base 2 and, therefore, the surface of silver base 2 may be etched. Foil 3-, however, should not be etched. The silver surface can be etched in various ways, for instance, by a hydrogen flame or else by certain chemicals, such as. nitric acid, sodium thiosulphate or ammonia sulpho cyanide.

After silver foil 3 has been peeled off from silver base 2 the glass shows certain surface irregularities as illustrated in Fig. 2. Therefore, it is preferred to keep silver base 2 at an elevated temperature until the glass has flown out in a layer of substantially uniform thickness under the influence of the surface tension of the hot glass. In this manner silver base 2 is provided with a glass film 6 of substantially uniform thickness as shown in Fig. 3. The whole procedure is preferably carried out at the temperature of molten glass which is about 800 centigrade, and the metal may be kept at a'temperature of from 750 to 850 centigrade.

It may be desired to use an electrically conducting glass for providing glass film 6. Such a glass may, for example, be a low melting glass which is electrically conducting. The dielectric layer 6 provided on silver base 2 is then of a semi-conducting character and may be used as a base for a conductive mosaic screen of the type referred to hereinabove. To that end glass layer 6 is usually provided with discrete photosensitive particles in a manner well known to those skilled in the art. It is of course to be understood that the process of the invention may be used for forming any glass film on any metallic support.

Another method of forming a glass film of uniform thickness on a metallic support has been illustrated in Figs. 4 to 6. Here the glass is first sandwiched between two metallic foils and then one of the metallic foils is peeled off again. In Fig. 4 there are shown two metallic foils I0 and II which preferably consist of silver and which may have a thickness of the order of magnitude of .001". Each of the silver foils I0 and II is coated with glass in the form of uniformly distributed unjoined glass beads I2. For this purpose foils I0 and I I may either be coated with hot glass or the glass may be applied by dusting or wet spraying.

Now metallic foils I0 and II are superimposed with their glass coatings or beads I2 in contact. This has been shown in Fig. 5. Then foils III and II are heated to an elevated temperature, and preferably to a temperature of 750 to 850 centigrade so that the glass between the foils is in a plastic state. Foils I0 and II are then pressed against each other in any suitable manner to provide for an intimate contact between silver foils III and II and glass layer I3 as shown in Fig. 6. At the same time the glass is formed into a layer I3 of uniform thickness which fills out the space between foils I0 and I I.

Silver foils III and II with glass beads I2 therebetween may, for instance, be rolled in the device shown in Fig. 8. In Fig. 8 there is provided a muflie I5 which is heated in any suitable manner. Rolls I6 and I I are provided in space I8 of muiiie I5. Roll I6 is journalled in bearings 20 and 2| arranged outside of muffle I5, and roll I! is journalledsimilarly in bearings 22 and 23. Rolls I6 and II are driven by toothed wheels 24 and 25 meshing with pinion 26 driven by electric motor 21. Foils I0 and II are rolled between rolls I6 and I! to reduce the thickness of the glass layer and to produce a glass layer of uniform thickglass layer l3. The thus obtained final product is shown in Fig. '7 and consists of silver foil l0 and glass layer 30 which is of uniform thickness. The dielectric layer 30 of semi-conducting glass may be used as a base for a conductive mosaic as explained hereinabove.

While there has been described what are at present considered the preferred embodiments of the invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention, and it is, therefore, aimed in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What is claimed is:

1. The method of forming a glass film on a metallic member having a plane surface which comprises the steps of applying glass to the plane surface of said member, covering said glass with a metallic foil, heating said member, glass and foil until said glass is in its plastic state, pressing said foil and said member against each other until said glass fills the space between said member and said foil in a layer of substantially uniform thickness, and removing said foil thereby to provide a glass film on said member.

2. The method of forming a glass-film on a metallic member having a plane surface which comprises the steps of heating said member to an elevated temperature, applying glass to the plane surface of said member, covering said glass with a metallic foil, keeping said member, glass and foil at said elevated temperature, pressing said foil and said member against each other until said glass fills the space between said member and said foil in a layer of substantially uniform thickness, and removing said foil thereb to provide a glass film on said member. I

3. The method of forming a glass film on a metallic base which comprises the steps of applying a relatively thick layer of glass to a surface of said base, covering said glass layer with a metallic foil, heating said base to an elevated temperature, pressing said foil against said base until said glass layer is in intimate contact with said base and said foil, pulling said foil away from said base, and simultaneously removing a portion of said glass layer adhering tosaid foil, thereby to reduce the thickness of said glass layer.

4. The method of forming a glass film on a metallic base which comprises the steps of applying a relatively thick layer of glass to a surface of said base, covering said glass layer with a -metallic foil, heating said base to an elevated temperature, pressing said foil against said base until said glass layer is in intimate contact with said base and said foil, pulling said foil away from said base and simultaneously removing a portion of said glass layer adhering to said foil, thereby to reduce the thickness of'said glass layer, and retaining said base and said reduced glass layer for a predetermined time at said elevated temperature to allow the glass to flow out in a film of substantially uniform thickness.

5. The method of forming a glass film on a silver base which comprises the steps of heating said silver base to the temperature of molten glass, applying a relatively thicklayer of hot glass 7 to a surface of said base, covering said glass layer with a silver foil, pressing said foil against said base until said glass layer is in intimate contact with said base and said foil, peeling said foil off from said base and simultaneously removing a portion of said glass layer adhering to said foil to reduce the thickness of said glass layer, and

retaining said base and said reduced glass layer for a predetermined time at said temperature to allow small variations of the thickness of the glass to equalize, thereby to obtain a glass film of substantially uniform thickness.

6. The method of forming a glassfilm on a silver base which comprises the steps of etching a surface of said silver base, heating said silver base to the temperature of molten glass, applying a relatively thick layer of hot glass to said etched surface, covering said glass layer with a silver foil, pressing said foil against said base until said glass layer is in intimate contact with said base and said foil, pulling said foil away from said base and simultaneously removing a portion of said glass layer adhering to said foil to reduce the thickness of said glass layer, and retaining said base and said reduced glass'layer for a predetermined time at said temperature to allow small variations of the; thickness of the glass to equalize, thereby to obtain a glass film of substantially uniform thickness.

7. The method of forming a glass film on. a metallic base which comprises the steps of heating said base to a temperature between 750 to 850 centigrade, applying a relatively thick layer of hot glass to a surface of said base, covering said glass layer with a metallic foil, pressing said foil against said base until said glass layer is in intimate contact 'with said base and said foil, pulling said foil away from said base and simultaneously removing a portion of said glass layer adhering to said foil to reduce the thickness of said glass layer, and retaining said base and said film for a predetermined time at said temperature to allow small variations of the thickness of the glass to equalize, thereby to obtain a glass film of substantially uniform thickness.

8. The method of forming a glass film on a metallic support which comprises the steps of coating a, metallic foil with glass, coating a second metallic foil with glass, superimposing said foils with theirglass coatings in contact, heating said foils until said glass is in its plastic state, rolling said foils until said glass coatings form a continuous glass film of substantially uniform thickness, and removing one of said foils.

9. The method of forming a glass film on a silver support which comprises the steps of coating a silver foil with glass, coating a second silver foil with glass, superimposing said foils with their glass coatings in contact, heating said foils substantially to the temperature of molten glass, rolling said hot foils until said glass coatings form a. continuous glass film of substantially uniform thickness, and removing one of said foils. I

10. The method of forming a glass film on a metallic support which comprises the steps of coating, a metallic foil with uniformly distributed unjoined glass beads, coating a second metallic foil with uniformly distributed unjoined glass beads, superimposing said foils with their glass coatings in contact, heating said foils until said glass is in its plastic state, rolling said foils until said glass coatings form a continuous glass film of substantially uniform thickness, and removing one of said foils.

11. The method of forming a glass film on a beads, superimposing said foils with their glass 6 coatings in contact, heating said foils to a temperature of between 750 to 850 centigrade, rolling said hot toils until said glass coatings form a continuous glass filmof substantially uniform 10 thickness, and removing one of said foils.

SANFORD F. ESSIG.

REFERENCES CITED The following references are of record in the flle of this patent:

UNITED STATES PATENTS Number Name Date 2,178,402 Miller Oct. 31, 1939 1,300,397 Holmstrom Apr. 15. 1919 

